Polyphosphazenes are polymers containing a plurality of --P&lt;.dbd.N--groups wherein substituents are bonded to phosphorus. The polyphosphazenes which are the concern of this invention are high molecular weight linear polyphosphazenes containing 50 or more of the above units and having molecular weights from about 10,000 up to 5,000,000 or higher. They are substantially linear and have little if any cross-linking. In general, they are soluble in benzene, toluene, cyclohexane, and tetrahydrofuran and are relatively insoluble in linear aliphatic hydrocarbons such as hexane or heptane. Groups substituted on phosphorus include phenoxy, alkylphenoxy, alkoxy and alkenylphenoxy (e.g. o-allylphenoxy) and the like.
Cellular plastics have been available for many years. One of the first of such materials was cellular rubber dating to the 1910-1920 period. Subsequently cellular compositions were made from latex, phenol-formaldehyde resins, urea-formaldehyde resins, PVC, polyurethane, cellulose acetate, polystyrene, polyethylene, epoxies, ABS resins, silicones and very recently polyphosphazenes. Polyphosphazene foams have very desirable properties in that they are highly fire resistant and when subject to direct flame do not produce toxic smoke which is encountered with many other common foamed materials, noteably polyurethanes.
Methods of making cellular polyphosphazenes are known. Various procedures are described in U.S. Pat. No. 4,026,838; U.S. Pat. No. 4,055,520; U.S. Pat. No. 4,055,523; U.S. Pat. No. 4,107,108; U.S. Pat. No. 4,189,413 and others. In general, the foams are made by mixing the polyphosphazene gum, a blowing agent and a peroxide or sulfur-type curing agent and heating the blended components to activate the blowing agent and cure the resultant foam.
Polyphosphazene copolymers which are substituted with both alkoxy and aryloxy substituents in the ratio of 4:1 to 2:3 are described in Reynard et al U.S. Pat. No. 3,856,712. Peroxide and sulfur cured fluoroalkoxy-substituted polyphosphazenes containing alkenylphenoxy substituents are described in Kyker et al U.S. Pat. No. 3,970,533. The amount of alkenylphenoxy ranges from 0.02 mole percent when using a peroxide cure to a maximum of 6 mole percent when using a sulfur cure. Aryloxy and alkoxy substituted polyphosphazenes which have 0.1-5 mole percent alkenylphenoxy substituents and are sulfur curable are described in Cheng U.S. Pat. No. 4,116,785.